This invention relates to hydrotreating of hydrocarbon streams. In particular it relates to catalytic hydrotreating. It also relates to the treating of residual oils and light cycle oil.
The increased demand for premium fuels, such as gasoline, diesel fuel, jet fuel, etc., coupled with the diminishing reserves of high-grade, sweet crude oils has dictated that the petroleum industry use greater proportions of heavier, lower quality, higher-sulfur containing crude oils in their operations in order to meet the needs of consumers. In addition to increased amounts of sulfur, many of the readily available crudes also contain increased quantities of metal compounds, nitrogen compounds and polycyclic hydrocarbons, such as asphaltenes. The undesirable components are generally found in the higher boiling components of the crudes and, hence, tend to become concentrated during distillation of the crude in the higher boiling fractions, particularly the bottoms fractions. These bottoms, unvaporized liquids remaining after distillation at atmospheric pressure or under vacuum, are generally called "residual stocks" or simply "resids." It is desirable to subject such resids to conditions of hydrodesulfurization, hydrodenitrogenation and/or hydrodemetallization prior to further processing, such as cracking, in order to convert the resids into higher valued products.
Hydrodesulfurization is a process intended primarily to convert the sulfur in organic sulfur compounds to hydrogen sulfide. Hydrodenitrogenation is a process intended primarily to convert the nitrogen in organic nitrogen compounds to ammonia. Hydrodesulfurization and hydrodenitrogenation will generally occur at the same time under similar process conditions if both organic sulfur compounds and organic nitrogen compounds are present in the feed stream. The hydrogen sulfide and/or ammonia can be removed from the feed stream after the hydrodesulfurization and/or hydrodenitrogenation process. Hydrodesulfurization and hydrodenitrogenation are processes which are typically utilized to remove sulfur and nitrogen from a hydrocarbon-containing feedstock which also contains organic sulfur compounds and/or organic nitrogen compounds to produce fuels which, when burned, will meet environmental standards. The processes can be applied to feed streams other than hydrocarbon-containing feeds if organic sulfur compounds and/or organic nitrogen compounds are present and the removal of sulfur and/or nitrogen is desired.
The earliest hydrodesulfurization and/or hydrodenitrogenation catalysts were bauxite and Fuller's earth. Later, catalysts containing cobalt oxide plus molybdenum oxide on alumina and nickel oxide plus tungsten oxide on alumina substantially replaced the earlier catalyst and these catalysts are still used very extensively. Another effective catalyst is a catalyst composition comprising cobalt, molybdenum, zinc, titanium and catalytic grade alumina disclosed in U.S. Pat. No. 4,287,050.
Hydrodemetallization is a process intended primarily to remove metals from a feed stream. Metals, such as vanadium and nickel, make further processing of the heavy fractions difficult since the metals generally act as poisons for catalysts employed in processes such as catalytic cracking. Hydrodemetallization has been accomplished in the past using a wide variety of catalysts under conditions of temperature and pressure and in the presence of hydrogen to selectively deposit the metals or metal-containing compounds on the surface of the catalyst. Hydrodemetallization is sometimes unintentially and undesirably accomplished, e.g., in hydrodesulfurization where the metals in the feed are deposited on the hydrodesulfurization catalyst resulting in deactivation and poisoning of the catalyst.
In the hydrotreating and hydrocracking of resids, benefit has been realized by mixing with the heavy residual stock a substantial portion of a light cycle oil (see, for example, U.S. Pat. No. 4,302,323). Light cycle oil is a distillate fraction boiling in the range of 400.degree.-650.degree. F. which contains high amounts of unsaturated compounds, generally polycyclic aromatic compounds. It is a lower valued product, especially because it is a poor blending stock for diesel fuel. In addition to a reduced cetane index, the light cycle oil imparts lower oxidative stability to any diesel fuel composition with which it is blended. Thus it is desirable to subject such fractions to conditions of hydrogenation which will at least partially saturate the aromatic rings in the polycyclic aromatic components of the fractions and thereby improve their value.
It is desirable to subject a mixture of resid and light cycle oil to conditions of hydrodemetallization, hydrogenation, hydrodesulfurization, and/or hydrodenitrogenation because in such a process the resid is converted to products of higher value for further downstream processing and the light cycle oil is converted to products of lower aromatic unsaturation for further downstream processing or for use directly in consumer products, e.g., blending with various motor fuels.
It is thus an object of this invention to provide a process for the hydrodemetallization, hydrogenation, hydrodesulfurization and/or hydrodenitrogenation of a mixture of resid and light cycle oil which exhibits higher activity and better selectivity than processes previously used.
Another object of this invention is to protect downstream catalyst from being poisoned.
Other objects and advantages of the invention will be apparent from the foregoing brief description of the invention and the appended claims, as well as the detailed description of the invention which follows.